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11.
MARIANNE GRAUERT SVANTE BJÖRCK STEIN BONDEVIK 《Boreas: An International Journal of Quaternary Research》2001,30(4):263-271
Presumed deposits of the Storegga tsunami have been recognized in a coastal lake situated 4 m a.s.l. on the island of Suðuroy, the Faroe Islands. The stratigraphy in the lake reveals a major erosion and redepositional event. The deposited material ranges from sand and sandy gyttja, with marine shell fragments and foraminifera, to gyttja with rip-up clasts, wood fragments and thin sand layers. Diatom analysis indicates that the deposit contains 5-8% polyhalobous (full marine) species, decreasing to 1-2% in the undisturbed lacustrine gyttja above. The tsunami event was dated to some time between 7300 and 6400 14 C yr BP. Lithostratigraphic profiles in the lake suggest that at least two large waves inundated the basin. The first and largest wave eroded most or all of the sediments previously deposited in the basin. The next wave caused minor erosion of the redeposited material. The waves deposited two generations of sand overlain by organic conglomerates, after which followed a unit of suspension material and normal lacustrine gyttja. 相似文献
12.
MELODY STEIN ANNIE ARNAUD‐VANNEAU THIERRY ADATTE DOMINIK FLEITMANN JORGE E. SPANGENBERG KARL B. FÖLLMI 《Sedimentology》2012,59(3):939-963
A major shift from Urgonian oligotrophic carbonate accumulation to orbitolinid‐rich mixed siliciclastic–carbonate deposition is observed near the Barremian–Aptian boundary in many sections both within and outside the shallow‐marine Tethyan Realm. This important facies change in the Swiss Helvetic Alps is documented here and interpreted in the context of general palaeoenvironmental change. To achieve this, a detailed micropalaeontological, sedimentological, mineralogical and geochemical study has been carried out on six sections across the upper part of the lower Schrattenkalk Member (Late Barremian), the Rawil Member (formerly ‘Lower Orbitolina Beds’, earliest Aptian) and the lowermost part of the upper Schrattenkalk Member (Early Aptian). The sediments of the Rawil Member exhibit inner‐platform facies with rudists, miliolids, orbitolinids and dasycladals to outer‐platform facies characterized by small benthic foraminifera, orbitolinids, crinoids and bryozoans. Stratigraphic trends in microfacies environments and the composition of microfossil assemblages, indicate that the Rawil Member includes a transgressive systems tract and the base of a highstand systems tract which are composed of an increasing number of parasequences in distal directions (five to nine in the sections studied here). The sea‐level rise discerned in the Rawil Member is coeval with increased detrital input and phosphorus burial, with maximum values up to 80 times and 21 times the background values in the subjacent part of the lower Schrattenkalk Member, respectively. Furthermore, the Rawil Member records the appearance of kaolinite, indicating a change towards tropical and more humid climate conditions. This change may have led to an increase in continental weathering rates and an associated increase in detrital and nutrient fluxes towards the ocean. The phase of climate change observed near the Barremian–Aptian boundary may have been triggered by a phase of intensified volcanic activity linked with the onset of the Ontong Java large igneous province and the Rawil Member may be the expression of a precursor episode to Oceanic Anoxic Event 1a in the shallow‐marine environment. 相似文献
13.
STEIN BONDEVIK JOHN INGE SVENDSEN GEIR JOHNSEN JAN MANGERUD PETER EMIL KALAND 《Boreas: An International Journal of Quaternary Research》1997,26(1):29-53
The statigraphy in 25 coastal lakes shows that most of the Norwegian coastline was impacted by a large tsunami about 7200 14 C BP. The methodology has been to core a staircase of lake basins above the contemporary sea level in several areas and to map the tsunami deposit to its maximum elevation. The tsunami was identified in the sedimentary record as an erosional unconformity overlain by graded or massive sand with shell fragments, followed by redeposited organic detritus. The greatest recorded runup along the coast (10–11 m above high tide) is found in areas most proximal to the Storegga slide scar on the Norwegian continental slope (Sunnmøre). To the north and south, runup is less, about 6–7 m at Bjugn (250 km north of Sunnmøre) and about 3–5 m in Austrheim (200 km to the south of Sunnmerre). This runup pattern supports the suggestion that the tsunami was generated by the Second Storegga Slide. The recorded runup heights are consistent within and between the investigated areas, and imply that the tsunami wave was not significantly influenced by the local topography, suggesting a very long wave length. The mapped runup estimates are in good agreement with a numerical model of the tsunami generated by the Second Storegga slide, and indicate that the slide was a single major event rather than a set of smaller slides. 相似文献
14.
JI Zhongqiang JIN Haiyan STEIN Ruediger LI Zhongqiao BAI Youcheng LI Hongliang ZHANG Yang CHEN Jianfang 《中国海洋大学学报(英文版)》2019,(3)
The organic matter(OM) preserved in Arctic Ocean sediments is of great importance to the global carbon budget. However, works that apply multiple proxies to determine the distribution and concentration of organic carbon(OC) in the surface sediments of the northern Bering and Chukchi Seas remain limited. Here a multiproxy approach based on bulk OM parameters and the branched vs. isoprenoid tetraether(BIT) index was used to investigate the distribution and sources of OM in the surface sediments of the northern Bering and Chukchi Seas. Binary and ternary mixing models were applied to trace the contribution of different OC sources to the total OC in the study area. The ?13 C values of the sediments provided by the binary model showed that the proportion of terrestrial OC fell in the range of 27.4%-79.8%(46.2% on average). The BIT index returned the lowest fraction(4.8%-27.3%, 12.0% on average). The ternary mixing model was employed to determine the plant-, soil-, and marine-derived fractions of the total OM. The ternary model showed that 11.5% ? 6.3%, 31.4% ? 9.5%, and 57.1% ? 12.4% of OM in the sediment of the study area was derived from soil, plants, and marine sources, respectively. The differences in OM composition between the west and east sides of the Chukchi Sea were controlled by OM inputs from key water masses(i.e., Anadyr Water and Alaska Coastal Water), river discharge, and the nutrient supply from the Pacific inflow that supports marine productivity. 相似文献
15.
AN INTERACTIVE COMPUTER/GRAPHIC-DISPLAY-TERMINAL SYSTEM FOR INTERPRETATION OF RESISTIVITY SOUNDINGS*
H. K. JOHANSEN 《Geophysical Prospecting》1975,23(3):449-458
A fast computer-procedure giving the apparent resistivity curve as well as the partial derivatives with respect to the layer-parameters is presented. It is based on the linear filter method developed by D. P. Ghosh in 1971. The sampling frequency is 10 points per decade, and 3 decades are covered. The maximum relative error is less than 10?3, and in most cases orders of magnitude smaller. The computation time on a CDC 6400 for one curve given in 30 points ranges linearly from .17s for a two-layer case to .36s for a ten-layer case. The procedure is used to plot master curves interactively on a graphic display terminal (Tektronix 4010) connected to the CDC 6400. By trial-and-error adjustments a set of layer-parameters is found, giving essentially the measured curve. 相似文献
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17.
MORTEN HALD TOR K. DANIELSEN STEIN LORENTZEN 《Boreas: An International Journal of Quaternary Research》1989,18(4):367-388
A benthic foraminiferal stratigraphy from the southwestern Barents Sea indicates that foraminifera were reworked and deposited in tills during the last glaciation. The deglaciation occurred in three main steps: (1) Presence of an Elphidium excavatum dominated assemblage > 13,300–12,000 B.P. (2), Nonion barleeanum dominated assemblage 12,000–10,000 B.P., and (3) establishment of a fauna similar to the modern one at 10,000 B.P. The transition from step 1 to step 2 indicates that the deglacial warming/incipient intrusion of Atlantic water was delayed in the southwestern Barents Sea compared with the western margin of the Norwegian shelf by approximately 1,000 years. Corrosive bottom water that formed during the last deglaciation causing carbonate dissolution may be due to poor ventilation or increased biogenic production accompanying the inferred oceanographic changes. 相似文献
18.
Tsunami sedimentary facies deposited by the Storegga tsunami in shallow marine basins and coastal lakes, western Norway 总被引：2，自引：0，他引：2
Sedimentary successions in small coastal lakes situated from 0 to 11 m above the 7000 year BP shoreline along the western coast of Norway, contain a distinctive deposit, very different from the sediments above and below. The deposit is interpreted to be the result of a tsunami inundating the coastal lakes. An erosional unconformity underlies the tsunami facies and is traced throughout the basins, with most erosion found at the seaward portion of the lakes. The lowermost tsunami facies is a graded or massive sand that locally contains marine fossils. The sand thins and decreases in grain size in a landward direction. Above follows coarse organic detritus with rip-up clasts, here termed ‘organic conglomerate’, and finer organic detritus. The tsunami unit generally fines and thins upwards. The higher basins (6–11 m above the 7000 year shoreline) show one sand bed, whereas basins closer to the sea level 7000 years ago, may show several sand beds separated by organic detritus. These alternations in the lower basins may reflect repeated waves of sea water entering the lakes. In basins that were some few metres below sea level at 7000 years BP, the tsunami deposit is more minerogenic and commonly present as graded sand beds, but also in some of these shallow marine basins organic-rich facies occur between the sand beds. The total thickness of the tsunami deposit is 20–100 cm in most studied sites. An erosional and depositional model of the tsunami facies is developed. 相似文献
19.
STEIN JOHANSEN 《Polar research》1998,17(2):125-146
Analysis of the wood anatomy of 481 driftwood specimens from Jan Mayen shows that Larix spp. constitute approximately 70% of the trees, while sawn logs are dominated by Pinus spp. by approximately 69%. A total of 356 driftwood samples from Jan Mayen and a small number of samples from Bjørnøya in the Barents Sea and the Troynoy Island in the Kara Sea were analysed by dendrochronological methods. A driftwood Pinus chronology was dated absolutely using chronologies from living trees of Pinus sylvestris in the lower proximity of the Angara River, a tributary of the Yenisey in Siberia. About 27% of the pine logs measured on Jan Mayen were found to originate in the same region, with end years concentrated in the 1940s and 1950s. A similar source was also found for Pinus driftwood logs on Bjørnøya and Troynoy. The results confirm and further delimit the source areas of the Yenisey driftwood established earlier from driftwood logs on Svalbard and Iceland. A subordinate source of both Pinus and Picea logs on Jan Mayen is northwest Russia, from the Kola Peninsula to the Pechora River. The Transpolar Drift Stream is believed to be the main distributor of driftwood from Siberian and northwest Russian sources to Jan Mayen, via the East Greenland Current. Dendrochronological dating reveals a strong, continuous input of ice-rafted driftwood from the Kara Sea. Radiocarbon datings from Jan Mayen show surface deposits of driftwood to be less than 500 years old, due mainly to extensive degradation of older wood and little or no land uplift. 相似文献
20.
Four relative sea-level curves from Edgeøya and Barentsøya are constructed based on 81 radiocarbon age determinations on carefully selected and levelled samples in raised beaches, mostly driftwood embedded in beach gravel. All the dates, covering the period from the deglaciation to the present, are calibrated to calendar years, and the sea-level curves are defined by fitting the data with a least square regression curve. The dates are internally very consistent, and the results are some of the most precise sea-level curves from the Arctic.
The four curves are quite similar, and from the marine limit at 85-90 m a.s.l. they show a rapid emergence (ca 40 mm/year), formed about 11,000 cal yrs BP (∼10,00014 C yrs BP). A minimum rate of emergence close to 8000 cal years ago is explained by a decreased rate in isostatic uplift parallel with a sustained rate of eustatic sea-level rise. During the last 7000 cal years, the emergence rate has decreased linearly. The uplift rates have been slightly higher on southern Edgeøya than further north during the last 7000 years. By comparing the sea-level curves from Storøya (ca 270 km to the north) and Hopen (ca 150 km to the south), we suggest that a memory of an earlier and larger glacio-isostatic downwarping in the southern Barents Sea is detected in the sea-level curves from Hopen and southern Edgeøya. 相似文献
The four curves are quite similar, and from the marine limit at 85-90 m a.s.l. they show a rapid emergence (ca 40 mm/year), formed about 11,000 cal yrs BP (∼10,000